Wireless communication systems are widely deployed to provide various types of communication such as voice and data. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), or some other modulation techniques. A CDMA system provides certain advantages over other types of systems, including increased system capacity.
A CDMA system may be designed to support one or more CDMA standards such as (1) the “TIA/EIA-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (the IS-95 standard), (2) the standard offered by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), (3) the standard offered by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in a set of documents including “C.S0002-A Physical Layer Standard for cdma2000 Spread Spectrum Systems,” the “C.S0005-A Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems,” and the “C.S0024 cdma2000 High Rate Packet Data Air Interface Specification” (the cdma2000 standard), and (4) some other standards.
One technique used to enhance performance, including system capacity and data throughput, is to lower the required transmit signal power by employing transmit diversity. Transmit diversity involves transmitting data on two or more antennas, where the geographical separation between the antennas leads to path loss characteristics that are independent from antenna to antenna. Thus, a receiving station can coherently combine signals from the transmit diversity antennas, and the noise introduced in the channel will not combine coherently, thus increasing the signal-to-noise ratio (SNR) received.
In some closed loop transmit diversity schemes, an example of which is proposed in the aforementioned W-CDMA specification, a mobile station sends phase adjustment information to the base station to adjust the phase of the signals being transmitted on one or more antennas. The phase can be adjusted such that when the signals from the various transmit antennas are received at the mobile station, they combine coherently. The mobile station uses the phase adjustment when demodulating forward link data. In accordance with the reverse link bit error rate, on occasion, the phase adjustment information will be incorrectly received at the base station. In response, the incorrect phase will be introduced to the data transmitted on the diversity antennas. If the mobile station does not recognize that the phase was not transmitted in accordance with the phase adjustment information, it will use the incorrect phase in demodulation, increasing the forward link error rate. This can be particularly troublesome at times when the reverse link bit error rate is relatively high.
Antenna verification techniques can be used to determine if the phase transmitted by the base station matches the phase requested by the mobile station. Improved antenna verification techniques allow for reduced forward link error rates for a given reverse link error rate, because the effect of an incorrectly received phase adjustment message can be reduced. There is therefore a need in the art for improved closed loop transmit diversity antenna verification.